obsidian hydration-rim dating

In archaeology, a method of dating artefacts made from the volcanic glass obsidian. Water molecules absorbed by inward diffusion through cut surfaces cause the outer areas of an obsidian article to convert to the mineral perlite. An object may be dated by measuring the thickness of this perlite – the hydration (combined with water) rim.

Only a molecule-thick water film is required at the surface to maintain the process, an amount available even in the near-arid zones of Egypt. Temperature, sunlight, and different chemical compositions cause variation in the hydration rate; therefore the method needs to be calibrated against an established chronological sequence for absolute dating. The method has been applied to many periods, including the Aztec age in Mexico, the pre-ceramic era of Japan (about 23,000 BC), and the tribal-war periods of Easter Island before the arrival of traders and missionaries in 1722. Obsidian hydration-rim dating was stimulated by the early research of Irving Friedman of the US Geological Survey from 1955.

Obsidian was used by early peoples to fashion tools and weapons in areas stretching from New Zealand and the Pacific to central Asia and the Mediterranean. It is associated with the development of complex trade networks and growth of domestication, such as at Çatal Hüyük, a Neolithic (New Stone Age) farming settlement in southern Anatolia.